Composite fine particles each of which is formed of a polymer and an inorganic material can enhance functions thereof due to combination of different properties which the polymer and the inorganic material have respectively. Further, by holding a functional substance in the composite fine particles, the application of the composite fine particles is expanded to wide fields such as medicines and cosmetics. Recently, with the sharp rise of environment awareness, a biomass raw material polymer such as a polylactic acid which is produced using a renewable resource such as plants as a raw material has been attracting attention. A polylactic acid is a material which is safely metabolically degradable in vivo. Calcium phosphate which is a main component of teeth and bones and has high biocompatibility has been attracting attention as a ceramic material.
Patent literature 1 discloses a spherical biodegradable polymer coated with calcium phosphate. Patent literature 2 discloses biodegradable polymer calcium phosphate composite nanoparticles. However, in the spherical biodegradable polymer coated with calcium phosphate disclosed in patent literature 1, calcium phosphate does not coat the whole surface of the spherical biodegradable polymer and hence, the spherical biodegradable polymer is not complete core-shell particles. Accordingly, even when a functional substance is encapsulated into the spherical biodegradable polymer coated with calcium phosphate, the spherical biodegradable polymer is decomposed into low molecules by hydrolysis so that the spherical biodegradable polymer cannot hold the functional material in a stable manner. In the same manner, biodegradable polymer calcium phosphate composite nanoparticles disclosed in patent literature 2 are also not complete core-shell particles so that biodegradable polymer is decomposed into low molecules by hydrolysis so that the biodegradable polymer calcium phosphate composite nanoparticles cannot hold the functional material in a stable manner.